Re: you want coverage? ;-) Re: Nikkor coverage

[zxiong@xxxxxxxxxxxxxxxxxxxxxx]

>Actually you should consider the circle if the lens were shifted 10mm in
>BOTH directions! So your lens would have to cover about 24x54 (the Nikkors
>both have fall off when shifted in the length of the film and Nikon
>recommends only shifting it 8mm). So doing the math says that the Nikon 28mm
>PC lens has about a 59mm circle.  not too bad for a 35mm lens.  but still
>not enough to cover more than a slit on a 120 panning camera.  So please
>explain how the 24mm Nikkor cover 120?

Hi Joe,

I thought people were talking about 120 slit cameras where you need only
56mm by 3 mm or so.  So if you have an image circle of 59 mm that will do
the job.  On the other hand.  I believe a lens is capable of covering a circlar
area, due to optical symmetry.  If it covers 24x54, if covers something slightly
less than 54x54.  I'm not familar with designs of any particular PC lenses, but
the pricipal should be the same. If a lens if shifted, it extends coverage to
a wider area. Then again, because the image circle is symmetric to the optical
axis, it must extend the coverage to an entire circle, even though the camera
opens only for part of it.

I came to this conclusion when I was puzzled by the tiny size of the Noblex 135U
lens which is capable of shifting 3 mm.  The lens itself is smaller than those 
on many point-and-shoot cameras, yet the image quality is exceptionally good and
shifting never produce any vegnitting.  I found out why when I reckoned with the
numbers.  The Noblex lens need only to cove 3x24 mm, far less than the 24x36
area required for other 35mm cameras. With 3mm shift it need only 6mm more of
coverage, which is only 3x30 mm.

Zonghou Xiong